half nelson

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A wrestling hold in which one arm is passed under the opponent's arm from behind to the back of the neck.

from the GNU version of the Collaborative International Dictionary of English.

• (Wrestling) A hold in which one arm is thrust under the corresponding arm of the opponent, generally behind, and the hand placed upon the back of his neck. In the full nelson both hands are so placed.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun wrestling A hold in which the wrestler applying the hold puts one arm under the arm of their opponent and applies pressure to the back of their opponents head or neck.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a wrestling hold in which the holder puts an arm under the opponent's arm and exerts pressure on the back of the neck